1. Field of the Invention
The present invention relates to a method for producing 2,6-di-tert.-butyl-4-cumyl phenol by reacting p-cumyl phenol with isobutylene. More particularly, the present invention relates to such a method wherein p-toluene sulfonic acid is used as a catalyst in the reaction.
2,6-DI-TERT.-BUTYL-4-CUMYL PHENOL PRODUCED ACCORDING TO THE PRESENT INVENTION IS A WHITE CRYSTALLINE COMPOUND USEFUL AS ANTIOXIDANT FOR VARIOUS PLASTIC MATERIALS AND AS AN INSECTICIDE HAVING PARTICULAR EFFECTIVENESS UPON MOSQUITO LARVAE.
2. Description of the Prior Art
Many methods have hitherto been known for introducing the tert.-butyl radical into the nucleus of phenols. There are known, for example, a method in which phenols are reacted with tert.-butyl chloride using aluminum chloride or phosphoric acid-boron trifluoride as catalyst, and a method in which phenols are reacted with isobutylene using a catalyst such as sulfuric acid, aluminum chloride, boron trifluoride-phosphoric acid, a cation exchange resin, phosphoryl trichloride, zinc oxide or Japanese acid clayzinc chloride. However, most of these known reactions are effective for introducing the tert.-butyl radical into the para position to the hydroxyl group of the phenol and are inadequate for introducing two tert.-butyl radicals into the ortho positions. Applicants are unaware of any prior art disclosure regarding application of these reactions for ortho position di-tert.-butylation of p-cumyl phenol. This has also been verified in investigations made by applicants which show the above reactions to be unfavorable, since the splitting off of the cumyl group at the para position has, due to the high activities of the catalysts, proceeded considerably under reaction conditions otherwise favorable for the tert.-butylation to take place. In addition, while the splitting off of the cumyl group can be repressed when the reaction conditions are moderated, for example, by decreasing the amount of catalyst, it is only possible to introduce one tert.-butyl radical into the ortho position, so that such measures also fail to introduce two tert.-butyl radicals into the nucleus of the phenol.
In addition to the reactions described above, other reactions have been known for introducing alkyl groups selectively into the ortho positions of phenols. For example, there is proposed in U.S. Pat. No. 2,831,898, an ortho-alkylation of phenols with olefins using a phenoxide of aluminum or magnesium as catalyst and it is known from the examples of Japanese published patent application Sho-47-3322 to introduce a tert.-butyl radical into the ortho position of a phenol with tert.-butyl alcohol using tellurium dioxide as catalyst. However, since both of these references teach a method in which either a mixture of mono- and de- substitution of the ortho position or mono-substitution alone is produced, they are not suited for obtaining solely the ortho-di-substitution. Moreover, if the catalyst of U.S. Pat. No. 3,831,898 is used to achieve ortho-alkylation of p-cumyl phenol, then the catalyst should be in the form of aluminum-p-cumyl phenoxide, which has been found by research of applicants to have very low catalytic activity so that the di-substituted product has not been obtained in suitable yield.
Furthermore, it is proposed in Bull. Soc. Chem. Belg., 26, 308 (1912) as well as in U.S. Pat. No. 2,865,966, to use p-toluene sulfonic acid as a catalyst for the alkylation of phenols. However, in these reactions, the para position of the phenol is alkylated. Furthermore, it is disclosed in U.S. Pat. No. 3,082,258 to use a hydrated product of methane disulfonic acid or methane trisulfonic acid as catalyst in producing 2,6-di-tert.-butyl-4-methyl phenol by the alkylation of p-cresol with isobutylene. Here, it was also taught that when p-toluene sulfonic acid or sulfuric acid is used as catalyst in such a disubstitution reaction, a product of inferior quality such as with coloration and odor will be obtained. However, if methane disulfonic acid or methane trisulfonic acid is used as catalyst in the alkylation of p-cumyl phenol with isobutylene, even though the splitting off of the cumyl group at the para position is considerably suppressed, the formation of 2-tert.-butyl-4-cumyl phenol, which is especially difficult to separate from 2,6-di-tert.-butyl-4-cumyl phenol as will be described hereinafter, can not sufficiently be reduced, so that the after treatment of the reaction product becomes very difficult and purification methods are uneconomical. In addition, the yield of the reaction may be lowered unfavorably, since p-cumyl phenol remains unreacted or the etherified product of p-cumyl phenol, i.e. tert.-butyl ether, is formed, both in considerable amounts.
As described above, it is impossible to obtain the disubstituted product at a high yield by the methods taught by the prior art because a considerable amount of mono-substitution product is formed and, at the same time, the splitting off of the cumyl group at the para position occurs.
Moreover, according to research by applicants, when the mono-substituted product is contained in the reaction product, it can hardly be removed by usual purification procedure such as recrystallization or distillation. In this case, the selective salt formation of the mono-substituted product by an alkali such as sodium hydroxide is also found ineffective. When the mono-substituted product is contained in the final product in a substantial amount, difficulties may arise; for example, it will cause a marked coloration of the product with the passage of time, because the mono-substituted product will be more readily oxidized when compared to 2,6-di-tert.-butyl-4-cumyl phenol and, therefore, lowering of the mono-substituted product during the reaction is very important.